In message <[email protected]>, dated Fri, 2 Feb 2007, Doug Smith <[email protected]> writes
>Thanks for the info on audio systems in theaters. I was thinking more >of safety problems of currents flowing. I have debugged a number of >audio hum problems over the years, some from the magnetic fields of >mains currents getting into sensitive audio inputs. > >The use you cite below is not a coupled bonding conductor. More of a >current shunt or bypass. I mentioned the normal main reason for installing it. Since it's disposed in the same was as a coupled bonding conductor, it works in the same way for surges and high frequencies. > When used for power mains current the voltage drop across the wire is >mainly across the resistance of the wire not the inductance so you >don't really have a canceling voltage induced by mutual inductance. Agreed; the mode of operation changes according to whether the inductance or resistance of the extra conductor is dominant. > >If the audio use were truly a coupled bonding conductor there would be >no problem with mains current flowing in the shield in the first place. >The shield would induce a canceling voltage by mutual inductance >eliminating the hum and an extra conductor would not be needed. The extra conductor is introduced in cases where the common-mode rejection of the connection is inadequate. It is indeed not needed if the equipment performance is as good as it can be. -- OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk There are benefits from being irrational - just ask the square root of 2. John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas [email protected] Mike Cantwell [email protected] For policy questions, send mail to: Jim Bacher: [email protected] David Heald: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. For more information please visit http://www.messagelabs.com/email ______________________________________________________________________
